The inside of the mater is engraved with a Quadratum Nauticum, the compass-points are indicated by the names of the winds in three bands with the cardinal directions marked as 'SEPTENTRIO', 'ORIENS', 'MERIDIES', 'OCCIDENS'. Reading north, east, south, west they are, centre band: 'Tramontana, Grecotramon{tana}, Greco, Greco leuante, Leua{n}te, Syrocco leuan{te}, Syrocco, Ostro syroc, Ostro, Ostrogarbin{o}, Garbino, Ponente garb{ino}, Ponente, Ponente maest{ro}, Maestro, Maestrotramon{tana}'. middle band: 'Aparctias, Aquilo, Cecias, Subsolanus, Eurus, Phenix, Auster, Libonotus, Africus, Zephirus, Corus, Circius'. outer band: Grecus, Sirocco, Libicus, Magistralis'. The outsides of the squares have scales from 0 ? to 90 ?, numbered by 30?, divided to 15? and subdivided to 3?. On top of the squares are the inscriptions (reading from the north): 'Longitudo maior vel Orient{alior}, Latitudo minor et Austra{lior}, Longitudo minor sive Occid{entalior}, Latitudo maior aut Boreali{or}'.

The throne, fixed to the rim by screws, consists of two foliate scrolls carrying two reclining male satyrs supporting a swiveling suspension in the shape of an armillary sphere. The swivel pin and the suspension ring are missing.

The rete, with construction marks on the reverse, follows the typical pattern of Arsenius type astrolabes. The names of 42 stars are given with their corresponding magnitudes, but without the planetary temperaments.

The ecliptic is marked with the usual Latin names of the zodiacal signs with their symbols. Each sign is divided to 30? with every 10? numbered divided to 5? and subdivided to single degrees.

Five sides of the three plates are marked with the circles for the equator (marked 'Circulus Aequinoctialis') and the tropics (marked 'Tropicus Cancri' and Tropicus Capricorni), azimuths for every 5? (numbered by 10?), almucantars for every 2? (numbered by 10?), the lines for the unequal hours (numbered 1 to 12) and the markings for the astrological houses in the manner of Regiomontanus (numbered 1 to 12). The 'Horizon Rectus' and the 'Horizon obliquus' are indicated and marked. North is marked as 'Septentrio'. The plates are laid out and marked for the following latitudes ('Pro elevatione poli'): 1a) 42 ('g<radus>); 1b) 43 ('g<radus>) 40 'm{inuta}'; 2a) 44, 45, 46; 2b) 50, 51, 52; 3a) 47, 48, 49; 3b) horizons for every 2? numbered by 10?.

The back bears several circular scales as follows (from the outside):

1) A 360? altitude scale, marked four times 0? to 90? starting at the east-west line, numbered by 5?, divided to half degrees by alternate shading;

2) A scale with the usual Latin names of the zodiacal signs, their symbols and figural representations, each sign is divided to 30?, numbered by 5? divided to single degrees by alternate shading;

3) An eccentric Gregorian calendar scale marked with the usual Latin names of the months and figural representations, divided to the corresponding number of days, every fifth day marked with divisions to single days in alternate shading.

Between the calendar scale and the zodiacal scale at the bottom is the signature 'P[star]Danfrie F.[star]'.

The bottom half of the vacant space inside these circles is taken up by a double shadow scale marked 'VMBRA RECTA' and 'VMBRA VERSA' to the bases 12 and 60 respectively, numbered by 3 and 5 respectively and divided to single digits. The right top half contains an horary quadrant for unequal hours numbered 1 to 6 to 12. In the centre is a solar cycle scale consisting of four concentric circles as follows (from the outside):

1) A year scale containing only the years 1600, 1601 and 1602.

2) The 28 year solar cycle marked 'CYCLUS SOLARIS' numbered 1 to 28, the fifth year corresponding to the year 1600 in the first scale.

3) and 4) The corresponding Dominical Letters (marked 'LITERA DOMINICAL') for ordinary years and leap years respectively, the letters B and A corresponding to the fifth year of the cycle and the year 1600. In the centre of the solar cycle scales is a blank escutcheon flanked by two stylized eagles and surmounted by a winged cherub's head surrounded by strapwork.

The rule and the alidade (sighting vanes missing) are both counterchanged and have foliate engraving. The pin consists of a long bolt and a circular nut with ridges.

The instrument was donated by Ferdinand de Rothschild in 1897 and is described in F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 117, no. 338.